1. Field of the Invention
The present invention relates to a toner, a developer and an image forming apparatus.
2. Description of the Related Art
In recent years, a toner is required to have a small particle diameter and high temperature-resistant offset property for a high-quality output image, low-temperature fixing property for energy saving, and heat-resistant storage stability for sustainability in a high-temperature and high-humidity environment during storage and transport of the toner. In particular, power consumption during fixing accounts for the majority of the power consumption in an image forming method, and improvement of low-temperature fixing property is very important.
Conventionally, a toner prepared by a kneading and pulverizing method has been used, where a toner composition obtained by melt-mixing and uniformly dispersing a colorant, a releasing agent and so on in a binder resin is pulverized and classified. It is difficult to reduce a particle diameter of the toner prepared by the kneading and pulverizing method, and at the same time, there have been problems such as insufficient quality of an output image thereof and high fixing energy due to its irregular shape and its broad particle diameter distribution. Also, when a releasing agent (wax) is added in order to improve fixability, the toner prepared by the kneading and pulverizing method is cracked at an interface of the wax during pulverization, and as a result, the wax exists predominantly on a surface of the toner. Thus, while a releasing effect is obtained, adhesion of the toner to a carrier, a photoconductor and a cleaning blade (filming) is likely to occur, and overall performance has not been satisfactory.
In order to solve the problems of the toner by the kneading and pulverizing method, various toner manufacturing methods by a polymerization method are proposed. A toner prepared by the polymerization method has a small particle diameter and a sharp particle size distribution, and it is possible to encapsulate a releasing agent.
As the toner manufacturing method by the polymerization method, for example, a method for manufacturing a toner from an elongation product of urethane-modified polyester has been proposed for the purpose of improving low-temperature fixing property and high temperature-resistant offset property (see Japanese Patent Application Laid-Open (JP-A) No. 11-133665).
Also, a toner having superior powder fluidity and transfer property as a toner having a small particle diameter and at the same time having superior heat-resistant storage stability, low-temperature fixing property and high temperature-resistant offset property has been proposed (see JP-A No. 2002-287400 and JP-A No. 2002-351143).
Also, a toner manufacturing method including an aging step has been proposed for producing a toner binder having a stable molecular weight distribution and obtaining both low-temperature fixing property and high temperature-resistant offset property (see Japanese Patent (JP-B) No. 2579150 and JP-A No. 2001-158819).
However, these proposed technologies cannot satisfy low-temperature fixing property of a higher level required in recent years.
Thus, for the purpose of obtaining low-temperature fixing property of a higher level, for example, there has been proposed a toner composed of a resin (a) which does not include a polyhydroxycarboxylic acid skeleton composed of an optically active monomer and a resin (b) having a polyhydroxycarboxylic acid skeleton composed of an optically active monomer, wherein the resin (a) is a polyester resin having crystallinity (see JP-A No. 2011-59603).
Also, a toner including a block copolymer composed of a crystalline polyester block and a non-crystalline polyester block as a core and a non-crystalline polyester resin as an outer shell has been proposed (see JP-A No. 2009-300848).
According to these proposals, low-temperature fixing of the toners may be achieved since the crystalline polyester resin quickly melts compared to the non-crystalline polyester resin. However, even though the crystalline polyester resin corresponding to an island in a sea-island phase-separation structure melts, the non-crystalline polyester resin corresponding to the sea as a majority does not melt. Since fixing cannot occur until both the crystalline polyester resin and the non-crystalline polyester resin melt to some degree, these proposed techniques cannot satisfy low-temperature fixing property of a higher level.
Accordingly, it has been desired to propose a toner which causes no filming and has superior low-temperature fixing property, high temperature-resistant offset property and heat-resistant storage stability.